1. Technical Field
The present invention relates to a method of manufacturing an anode core-shell complex for a solid oxide fuel cell using a hydrazine reducing agent and a surfactant. Particularly, core-shell powder including spherical nano-sized nickel as a core and stabilized zirconia particles as a shell is manufactured using a hydrazine reducing agent and a surfactant, and when the powder is used as an anode, nickel and stabilized zirconia are uniformly distributed and have a dense fine structure. Accordingly, an electrochemical reaction and long-term performance of the anode for the solid oxide fuel cell are improved.
2. Description of the Related Art
Currently, a demand for a novel energy source is growing in accordance with gradual depletion of fossil raw materials. A solid oxide fuel cell of directly converting chemical energy into electric energy has high energy conversion efficiency, and is capable of adopting various fuels by internal reforming thereof and being hybridized with a gas turbine to have improved efficiency. Accordingly, the solid oxide fuel cell receives attention as a next-generation energy source.
Generally, the solid oxide fuel cell has a structure where a cathode, a solid electrolyte, and an anode are sequentially laminated. Yttria-stabilized zirconia (YSZ) stabilized by adding nickel or nickel oxide is used as a typically used anode. Further, porous LSM is used as the cathode, and stabilized zirconia is used as the solid electrolyte. In the solid oxide fuel cell, oxygen provided from the cathode moves through the solid electrolyte and is electrochemically reacted with hydrogen of the anode to cause electromotive force.
A mixture of nickel or nickel oxide and yttria stabilized zirconia (8 mol % Y2O3, 92 mol % ZrO2) may be simply mixed by a dry or wet method. However, since attractive forces between powders are different from each other, the two powders are not dispersed simultaneously in the same dispersion condition but agglomerate. Particularly, an agglomeration property of the nano-sized powder for reducing surface energy causes nonuniformity of a fine structure of the anode after sintering. Accordingly, a conductive path is broken or becomes a by-path to reduce electric conductivity.
Nonuniformity of distribution of crystal grains and pores by a geometric shape, a size, and the degree of agglomeration of a raw material constituting the anode negatively affects electric conductivity, fuel transmittance, coarsening of nickel, and activity of a triple phase boundary to reduce durability and an output property of an end cell. A heat cycle, a long-term operation, and oxidation and reduction reactions at the anode reduce coarsening of nickel and a reaction area of the triple phase boundary formed of nickel, stabilized zirconia, and the pore. Therefore, electrochemical activity is reduced. Finally, there is a problem in that an output of the end cell is reduced.
Efforts have been continuously made to solve the problem. Korean Patent Application Publication No. 2012-0121570 discloses a technology of manufacturing anode powder having improved long-term stability, heat cycle stability, redox stability, and mechanical properties according to suppression of a volume shrinkage in a reduction atmosphere by mixing nickel (Ni) metal powder used as a core and stabilized zirconia powder used as a shell at a high speed to manufacture powder having a nickel-stabilized zirconia core-shell structure, and heat-treating the manufactured powder at 1300 to 1500° C. to form a nano-complex structure in which crystal grains of nickel and stabilized zirconia have a uniform nano size and a continuous network therebetween.
As a method of manufacturing the solid oxide fuel cell, in the case of a planar type, generally, a method of forming a support layer electrolyte or an anode supporting a shell by tape forming or extrusion forming, laminating another constitution component thereon by tape forming or coating a slurry, and performing firing at high temperatures to manufacture the solid oxide fuel cell is performed. In this case, generally, a method of firing at least two of constitution materials such as the anode, the electrolyte, and the cathode together at high temperatures is performed in order to simplify a manufacturing process and reduce a manufacturing cost. In the case of a tubular type, each slurry of materials constituting the electrode and the electrolyte is applied on a tubular support, and then fired at high temperatures to manufacture the solid oxide fuel cell.
The present applicant has filed an application with Korean Patent Application No. 2012-0054442 entitled “a method of manufacturing a nickel/stabilized zirconia core-shell complex where metal ions for a solid oxide fuel cell anode are solid-solved” relating to a method of manufacturing a metal-solid-solved nickel/stabilized zirconia core-shell complex for a fuel cell, in which a known nickel-stabilized zirconia mixture having excellent electrical conductivity and mechanical strength was used, a small amount of metal such as cobalt, iron, copper, and chrome was solid-solved to lower a carbon deposition ratio in a methane atmosphere, and a core-shell structure was provided to further improve stability at high temperatures.
The present inventors invented a method of manufacturing a core-shell complex and a uniform mixture using a hydrazine reducing agent and a surfactant in order to improve performance of a solid oxide fuel cell through a subsequent study, thereby accomplishing the present invention.